Downloadable Filters for a Visual Prosthesis

ABSTRACT

The present invention is a method of neural stimulation and more specifically an improved method of providing flexible video/image possessing in a visual prosthesis by providing downloadable video filters. In a visual prosthesis, the input video image will, for the foreseeable future, be higher resolution than the output stimulation of the retina, optic nerve or visual cortex. This is due to limits of electrode array technology and the rapid advancement of video camera technology. It is therefore, advantageous to apply video processing algorithms (filters) to help provide the most useful information to the lower resolution electrode array. Different filters are more effective in different environments and for different subjects. Furthermore, filters will continue to improve over time. Examples of situation dependent filters include reverse image, contrast increasing, edge detection, segmentation using chromatic information and motion detection. Filters loaded in the video processing unit may be selected dynamically to suit the situation or the user&#39;s preference. It is therefore advantageous to provide flexibility in applying filters. However, it is also important to maintain the security necessary for a medical device. The present invention provides for an external (not implanted) video processing unit with downloadable video filters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims priority toU.S. application Ser. No. 11/523,257, filed Sep. 18, 2006, forDownloadable Filters for a Visual Prosthesis, which claims the benefitof U.S. Provisional Application No. 60/718,096, “PC Downloadable ImageProcessing Filter for Retinal Prosthesis”, filed Sep. 16, 2005, thedisclosure of which is incorporated herein by reference. Thisapplication is related to U.S. patent application Ser. No. 11/413,771,filed Apr. 28, 2006, for Method and Apparatus to Provide Safety Checksfor Neural Stimulation, which is incorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to neural stimulation andmore specifically to an improved method of providing flexible videopossessing in a visual prosthesis by providing downloadable videofilters.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising a prosthesis foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases such as retinitis pigmentosaand age related macular degeneration which affect millions of peopleworldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across retinal neuronal cell membranes, which can initiateretinal neuronal action potentials, which are the means of informationtransfer in the nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

Some forms of blindness involve selective loss of the light sensitivetransducers of the retina. Other retinal neurons remain viable, however,and may be activated in the manner described above by placement of aprosthetic electrode device on the inner (toward the vitreous) retinalsurface (epiretinal). This placement must be mechanically stable,minimize the distance between the device electrodes and the retinalneurons, and avoid undue compression of the retinal neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated a cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 uAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

It is known that neurons respond best to change in stimuli. The retina,if continuously stimulated in a consistent manner, will slowly becomeless and less sensitive to the stimulus. This causes the perception of aconstant visual image to gradually disappear. Those with normal visionare unable to perceive this effect because the eye constantly moves,motions called jitter or microsaccades. A normal retina has a resolutionof approximately four million light transducer cells (rods and cones),hence it requires a minute movement to change the light intensity castupon a given light transducer.

A retinal prosthesis, according to the present invention, has twodisadvantages. First, the resolution of an electrode array applied tothe retina is significantly lower than the resolution of a healthyretina, requiring a greater movement to move an image from one electrodeto the next electrode, as compared to one cone to the next cone.Further, a head mounted camera does not have the natural jitter ormicrosaccades of an eye. Therefore it is necessary to achieve therequired change in another manner.

It is also known that some neural processing is done within the retina.Hence, a continuously stimulated cone will not result in a continuoussignal to the brain. Ganglion and bipolar cells pass along this changein information more readily than constant information. In a diseasedretina, rods and cone cannot be stimulated, since they are dead.Electrically stimulating cells further along the neural pathway,bypasses some of the neural processing. This processing must besimulated electronically to gain normal brain stimulation.

The ability to perceive a constant image or image contrast is necessaryto the design of a visual prosthesis.

SUMMARY OF THE INVENTION

The present invention is a method of neural stimulation and morespecifically an improved method of providing flexible video/imagepossessing in a visual prosthesis by providing downloadable videofilters.

In a visual prosthesis, the input video image will, for the foreseeablefuture, be higher resolution than the output stimulation of the retina,optic nerve or visual cortex. This is due to limitations of electrodearray technology and the rapid advancement of video camera technology.It is therefore, advantageous to apply video/image processing algorithms(filters) to help provide the most useful information to the lowerresolution electrode array. Different filters are more effective indifferent environments and for different subjects. Furthermore, thesefilters will continue to improve over time.

Examples of situation or environment dependent filters include reverseimage, contrast increasing, edge detection, segmentation using chromaticinformation, and motion detection. Many other filters will be useful inproviding the best possible image to a subject. Filters loaded in thevideo processing unit may be selected dynamically to suit the situationor the subject's preference.

It is therefore advantageous to provide flexibility in applying filters.However, it is also important to maintain the security and integritynecessary for a medical device. The present invention provides for anexternal (not implanted) video processing unit with downloadable videofilters.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of the hardware supporting downloadablefilters.

FIG. 2 depicts of block diagram of the filter download code space.

FIG. 3 is a flow chart showing the filter download process.

FIG. 4 is a flowchart of the stimulation process using downloadablefilters.

FIG. 5 is a perspective view of the implanted portion of the preferredvisual prosthesis.

FIG. 6 is a side view of the implanted portion of the preferred visualprosthesis showing the fan tail in more detail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

Referring to FIG. 1, images from a video camera (not shown) aretransferred to an input buffer 12. The image is applied to the filter 14which includes code 16 and data 18 to generate an image in an outputbuffer 20. All of this takes place in a digital signal process (DSP) 10.While the preferred embodiment includes a DSP, it would be clear to oneof skill in the art that the functions described here could beaccomplished by a microprocessor or even separate components.

Referring to FIG. 2, the DSP 10 includes memory space for both theexecutable code (algorithm) and data (parameters such as transformationmatrices). The down loadable filters have fixed spaces for code 22 anddata 24. Note that the down loaded algorithms and parameters areassigned to, and limited to, specific memory locations. As a medicaldevice, a visual prosthesis must have security and safety checks whichprevent over stimulation of the neural tissue. Dedicated memory space,authenticity checks, and error checks, provide for the safety of thepatient. However, the system must be designed such that no filter, nomatter how mis-designed, can bypass important safety checks and endangerthe heath of the patient. These safety checks are described in U.S.patent application Ser. No. 11/413,771, filed Apr. 28, 2006 for Methodand Apparatus to Provide Safety Checks for Neural Stimulation, which isincorporated herein by reference.

Referring to FIG. 3, the download process begins by interrupting thestimulation process 42 as shown in FIG. 4. This is necessary for safetyto insure that no stimulation is attempted with a partially loadedfilter. Next the filter is downloaded from a linked computer (not shown)44. Many peer to peer communication protocols are well known and can beused for this purpose. The preferred embodiment uses a Universal SerialBus (USB) interface. Next, a cyclic redundancy check (CRC) is preformed46 to ensure data integrity. If there are any errors, the filterdownload is restarted or retried.

Next, the system performs a version control check 48. Each filterincludes a table of compatible firmware versions. If the filter isincompatible with the firmware version an error message is returned tothe linked computer 50 and the download process is terminated. If theversion is compatible, a space check is performed 52. The DSP has finitefixed space for code and data. If either is too large, an error messageis returned to the linked computer 54 and the download process isterminated. If there is adequate space for code and data, the filter isdownloaded and written to non-volatile memory 56. In the preferredembodiment non-volatile memory is flash memory. The filter is thenwritten to DSP memory 58 and stimulation is restarted 59. Since theinternal memory in the DSP is volatile, the flash memory provides backupwhen power is lost.

FIG. 4, shows the stimulation process. When a new frame is ready, themaster process sends a process request to the filter process. The filterprocess continuously checks for a new process request 70. This is doneby a time slice method in the DSP. Hence, the filter is not tying up theprocessor looking for process requests. If there is a process request,the filter process checks to see if the filter is ready 72. The filtermay not be ready if it is in the process of a download as described withrespect to FIG. 3. If ready, the system retrieves the image from aninput buffer 74, processes the image according to the filter 76, andsends the resulting image to the output buffer 78. Finally, it sends asignal that the image is ready in the output buffer and returns to waitfor a new process request.

FIG. 5 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. An electrode array 110 is mounted by aretinal tack or similar means to the epiretinal surface. The electrodearray 110 is electrically coupled by a cable 112, which pierces thesclera and is electrically coupled to an electronics package 114,external to the sclera.

The electronics package 114 is electrically coupled to a secondaryinductive coil 116. Preferably the secondary inductive coil 116 is madefrom wound wire. Alternatively, the secondary inductive coil may be madefrom a thin film polymer sandwich with wire traces deposited betweenlayers of thin film polymer. The electronics package 114 and secondaryinductive coil 116 are held together by a molded body 118. The moldedbody 18 may also include suture tabs 120. The molded body narrows toform a strap 122 which surrounds the sclera and holds the molded body118, secondary inductive coil 116, and electronics package 114 in place.The molded body 118, suture tabs 120 and strap 122 are preferably anintegrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 116 and molded body 118 are preferably ovalshaped. A strap can better support an oval shaped coil.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. It is an advantage of the present design, that the entireimplanted portion of the prosthesis is attached to and supported by thesclera. By placing the device under the rectus muscles with theelectronics package in an area of fatty issue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 6 shows a side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the fan tail 124. When implantingthe retinal prosthesis, it is necessary to pass the strap 122 under theeye muscles to surround the sclera. The secondary inductive coil 116 andmolded body 118 must also follow the strap under the lateral rectusmuscle on the side of the sclera. The implanted portion of the retinalprosthesis is very delicate. It is easy to tear the molded body 118 orbreak wires in the secondary inductive coil 116. In order to allow themolded body 18 to slide smoothly under the lateral rectus muscle, themolded body is shaped in the form of a fan tail 24 on the end oppositethe electronics package 114.

Accordingly, what has been shown is an improved method of making aneural prosthesis and improved method of stimulating neural tissue.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. In particular, thepreferred embodiment describes a retinal prosthesis for artificialvision. It should be obvious to one skilled in the art that theinvention has broad applicability to other types of neural stimulation.It is therefore to be understood that within the scope of the claims,the invention may be practiced otherwise than as specifically describedherein.

1. A method of electrically evoking artificial vision comprising:determining a situation dependent video filter; storing said situationdependent video filter in a video processing unit; collecting videoinformation; applying said situation dependent video filter to saidvideo information in said video processing unit; and stimulating visualneurons according to said video information.
 2. The method according toclaim 1, wherein said situation dependent video filter is a reverseimage filter.
 3. The method according to claim 1, wherein said situationdependent video filter is a contrast increasing filter.
 4. The methodaccording to claim 1, wherein said situation dependent video filter isan edge detection filter.
 5. The method according to claim 1, whereinsaid situation dependent video filter is a movement detection filter. 6.The method according to claim 1, wherein said situation dependent videofilter is a down sampling filter.
 7. The method according to claim 1,wherein said step of storing includes error checking.
 8. The methodaccording to claim 1, wherein said step of storing include authenticitydetection.
 9. The method according to claim 1, wherein said step ofstoring includes storing executable code and data.
 10. A visualprosthesis system comprising: A computer for storing a plurality ofalterative sets of video filter information; A video input device; Avideo processing unit including means for receiving at least one of saidalternative sets of video filter information from said computer, meansfor receiving video data from said video input device, and means forprocessing said video data according to said at least one of saidalternative sets of video filter information; and An array of electrodesstimulating visual neural tissue according to said video data processedaccording to said at least one set of alternative video filterinformation.